overnight anchor

Agree much of that Deleted User. All a bit imho but I too am pretty sure that virtually none of a mobo's shearing around its anchor actually gets seen as a chain angle change at the anchor. Different for sailboats though. While I would beg to differ with GSkip's claim that Bernoulli makes aeroplanes fly and shower curtians blow in (let's not go there, too much thread drift!) I agree with some of his Bernoulli on boats shearing at anchor

I suggest boats shear around the anchor because

(a) sometimes flapping with windshift (which any dinghy racer will tell you happens a lot, +/-5 degrees).

(b) becuase of gusting. In between gusts the boat moves forward under weight of chain. In gusts it blows back but as it does so it naturally starts to turn broadside to wind, as it drifts downwind. It gets partway then the anchor chain pulls the bow round, and it overshoots, so see-sawing.

(c)Finally, and this is where Bernoulli applies, a sailboat that is at an angle to the wind can literally sail with its hull as the aerofoil and the keel as the keel. Some tension in the chain keeps it nicely 45 deg (say) to the wind, so as to trim the rig. It will then sail forwards towards a point at the side of its anchor, till it sort of tacks and repeats the performance, hence see-saw sailing around the anchor. This happens a bit on mobos, but is more of a sailboat thing becuase mobos have lousy keels. When this happens it can break the anchor out. Indeed, this was the accident investigator's conclusion on Mirabella V's grounding in 2004.
 
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a sailboat that is at an angle to the wind can literally sail with its hull as the aerofoil and the keel as the keel.

[/ QUOTE ]Can't see why the keel should affect that.
Unless you're assuming that tide is moving together with the wind, or am I missing anything else?
 
??? I am confused how you could think a keel is not relevant??? I assuming no tide. For a boat to sail forwards towards (somewhat) its own anchor, ie upwind, it needs a keel effect. Just like a sailboat beating. A sailboat will do this better cos it has a better keel. A tea-tray will never sail towards its own anchor
 
FWIW, I deliberatley choose not to use one of those overnight. They cut out the noise of the anchor chain rubbing on the bow roller, but at night I want to hear that as it tells me the weather is getting worse! Just imho

As a matter of engineering, it seems to me there is no problem leaving the anchor load on the winch, so giving the winch a rest isn't a reason to use a snubber. Many captains disagree, and take loads off their bow and stern winches when moored, but there isn't any scientific or engineering reason to do that I'd suggest (happy to be corrected if someone can proffer a good reason to do it!)
 
Whoops. I read your post quickly and understood that you were mentioning Bernoulli for both the hull and the keel...
 
Well, it also depends on the winch/chains arrangement.
Actually, I'd still do that with the typical winch of a planing boat, but there are indeed good reasons to do that with winches like mine (see pic above, and also the avatar), where you have no bow roller.
Firstly, any snatch can create a very strong downward pull. And if you just stand near the winch when weighing an heavy anchor, and feel with your feet how a (rather bulky) deck can flex, you surely don't want to see what happens with a multiple of such force.
Secondly, with such anchor/chain rigging, for as long as you're anchored, it's just one specific ring of the anchor chain which is continuously grinding against the corner of the s/s tube (sorry, dunno the specific English term) where the chain pass through. Now, I don't know how long it would take to "saw" that ring, but I don't want to discover it either!...
 
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I have often wondered the same thing. I'd love to anchor one night.
Is there anywhere in Poole harbour thats safe for an overnight anchor? How about Studland Bay, anyone done there?


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Endlessly. We're so blase about it in Studland we just rock up, drop the pick and that's it. It's got to be the best holding for miles. Get out there and enjoy it!

Simple version:
<ul type="square"> [*]Studland has perfect holding [*]Check the tide when you get there and work out how far off high water you are and hence how much the tide will rise [*]Add the predicted rise to your current depth [*]Let out 4 times that depth of chain [*]Open a bottle, have something to eat, go to sleep [*]End [/list]
 
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I also have been looking for some device that will hold the chain. I'm told that there is one. But never found it. A hook through the chain, looks like the weekest link to me. I wrap the chain round a cleat, if I think it's needed.

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Called chain hooks - hard to describe but you find them in the swindlers' catalogues. I have ours in the middle a length of warp with a rubber snubber either side of it. Set the anchor and make sure you're happy, then hook the hook into the chain and make the warp off to a cleat either side of the roller, then pay out the anchor rode until there's a nice loop of slack chain and the strain is taken by the warp/hook/snubbers. You can see the setup here:
Studland1.jpg
 
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I've just been told on shutyerbut, that anchoring in Studland is imposible, without the "right" anchor.

I can only think, folk are stinjy with the chain.

[/ QUOTE ]Bollocks. You can anchor in Studland Bay without an anchor, the holding's that good! We've woken up before now and looked over the bow to see the anchor still lying on its side because a) the water's that clear and b) we had enough chain out that the anchor never even needed to set...
 
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As a matter of engineering, it seems to me there is no problem leaving the anchor load on the winch, so giving the winch a rest isn't a reason to use a snubber. Many captains disagree, and take loads off their bow and stern winches when moored, but there isn't any scientific or engineering reason to do that I'd suggest (happy to be corrected if someone can proffer a good reason to do it!)

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Hmm, I agree with you on the typical stern winch as they're usually ratchet devices. However, on my windlass, its just a friction clutch which I'd rather not trust as it does ease over time and occasionally needs tightening.
 
All read pretty well and comprehensive but as you say a little raggy orientated.

I have experience of all four anchors mentioned on motor and sail. Nobody makes a bad one imo but some are more suited to different bottom conditions. The bruce holds well but can be a sod to retrieve anywhere near rocks. CQR is the best well proven standard and favoured by most old sea dogs with sail background.

For motor boating my favourite is the Delta, never misses a beat and easy to retrieve and would be my first choice.

from you blog:
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Many boats use as their primary system a rope/chain combination in which the chain leader is only a boat length, or so, long. This introduces the spectre of a parting ropeto-
chain splice and chafe or laceration on rocks, coral, or bow-roller. A windlass is still
necessary to handle the chain leader but there is the complication of switching from
chain to rope gypsy during recovery. An all-chain rode never leaves the windlass,
giving great control

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Sorry, but this isn't really true on most Mobo windlass'. Chain to rope works very well provided you have the space to let out the scope. With vertical windlass' the chain gypsy will take chain to rope without lifting off to a second capstan! You just need the right (as in 14mm rope with 8mm chain) 3-ply rope 'chain spliced' correctly and this will then run straight through the chain gypsy and still stow on its own.

In favourable conditions, RYA standards used to be scope 3:1 chain and 5:1 for rope. Over the past 25 years this has generally become greater due to some inexperienced boaters trying to cut corners. If you need more than this you probably shouldn't be there overnight anyway. I use 4:1 with chain only and a little more if its windy. This gives a longer horizontal pull from the catenary curve and reduces snatch if its choppy. I also use a rope strop and chain hook to keep the load of the windlass itself.

We've enjoyed many peaceful nights at anchor because my anchor alarm is silent! /forums/images/graemlins/grin.gif

Enjoy it and just build your confidence as suggested by Neale above.
 
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A hook through the chain, looks like the weekest link to me. I wrap the chain round a cleat, if I think it's needed.

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If you have a look at the strength of ropes, you'll find they are often stronger than the chains we use. The chain hook is certainly stronger than the galvanised anchor chain on our boat and probly yours too.
 
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If you need more than this you probably shouldn't be there overnight anyway.

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Do you mean in general, mobos, or those new'ish to anchoring overnight?

Richard
 
quote; Some very interesting info gskip but I've always wondered about whether a 2 anchor set up as you describe is actually safer.

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totally agree. unless it is impossible to find a space with swinging room, my kedge stays in the locker. We also are in the med, but if in tidal water then I think the same problem arises with the change of tide. You end up held by a small and less effectual anchor. a reversal of tide and/or wind and you could easily drag.
 
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(b) becuase of gusting. In between gusts the boat moves forward under weight of chain. In gusts it blows back but as it does so it naturally starts to turn broadside to wind, as it drifts downwind. It gets partway then the anchor chain pulls the bow round, and it overshoots, so see-sawing

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IMHO, that is the main reason that mobos shear around more at anchor than saily boats. They are higher sided and carry more windage and thus adopt a beam on attitude to the wind more easily. And the reason that they shear one side to the other is that when the boat is beam on, it is blown downwind until the anchor chain tightens and brings the bow into the wind and this sets up a rotation movement which swings the stern around to the other side. As you say, the chain tightens and then releases slightly which allows the boat to go beam on to the wind again but since the stern has swung to the other side, it is the opposite side of the boat which is beam on. And then it all happens again and you get the side to side shearing

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All a bit imho but I too am pretty sure that virtually none of a mobo's shearing around its anchor actually gets seen as a chain angle change at the anchor.

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I have made a point of snorkeling out to the anchor in windy conditions (I'm an anorak) just to observe how the chain behaves and, even when the boat is shearing quite violently, most of that movement is definitely absorbed by the catenary effect of the chain and very little lateral force is applied to the anchor and, if there is enough chain laid out, definitely zero vertical force. IMHO, in the light to moderate winds that we mobos tend to anchor in, the anchor does very little in terms of holding the boat, and most of the holding force is provided by the weight of chain lying on the seabed (which with a 3:1 scope is usually more than 50% of the chain) and the catenary effect. With a shorter scope or a rope/chain or an all rope warp, then the anchor has to provide a lot more of the holding power
 
Agree with rickp in that when the chain gypsy is friction held, you are reliant on that friction alone to stop the gypsy rotating so it is good practice to take the load off the winch. I do agree that the winch fixing is likely to be stronger than the adjacent cleat fixings so, if a rope snubber is used, it actually makes more sense to tie it to the winch rather than a cleat
 
OK fair enough to use a snubber to solve a dodgy clutch. But the fact it's a friction clutch per se is not a reason to label it unreliable. Your car's brakes are friction clutches. The round turns and figure 8's that you attach snubber to cleat with work 100% on friction. Friction holding is a good reliable predictable thing and a properly maintained and tightened friction clutch should be fine. If it does fail (a) you'll hear it and (b) what's the worst that'll happen - your chain will slowly pay out until the rope at the bitter end holds the boat, which is fine.
 
Well, actually my snubbers have nice loops on the ends so it's definitely not friction that holds them onto the cleats although I guess it's friction that holds the loops together /forums/images/graemlins/smile.gif
Agree with your analogy by why risk drifting into the boat behind for the want of a bit of rope and 2 minutes work?
 
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